Field of the Invention
The present invention relates to xylanase variants, polynucleotides encoding the variants, methods of producing the variants, and methods of using the variants.
Description of the Related Art
Plant cell wall polysaccharides constitute approximately 90% of the plant cell wall and can be divided into three groups: cellulose, hemicellulose, and pectin. Cellulose represents the major constituent of call wall polysaccharides. Hemicelluloses are the second most abundant constituent of plant cell walls. The major hemicellulose polymer is xylan.
Xylan is a polymer of D-xylose linked by beta-1,4-xylosidic bonds. Xylan can be degraded to xylose and xylo-oligomers by acid or enzymatic hydrolysis. Enzymatic hydrolysis of xylan produces free sugars without the by-products formed with acid (e.g., furans).
Enzymes capable of degrading xylan and other plant cell wall polysaccharides are important for the food industry, primarily for baking and in fruit and vegetable processing such as fruit juice production or wine making, where their ability to catalyze the degradation of the backbone or side chains of the plant cell wall polysaccharide is utilized (Visser et al., Xylans and Xylanases, Proceedings of an International Symposium, Wageningen, The Netherlands, Elsevier Science Publishers, 1992). The biodegradation of the xylan backbone depends on two classes of enzymes: endoxylanases and beta-xylosidases. Endoxylanases (EC 3.2.1.8) cleave the xylan backbone into smaller oligosaccharides, which can be further degraded to xylose by beta-xylosidases (EC 3.2.1.37). Other enzymes involved in the degradation of xylan include, for example, acetylxylan esterase, arabinase, alpha-glucuronidase, ferulic acid esterase, and p-coumaric acid esterase.
Other applications for xylanases are enzymatic breakdown of agricultural wastes for production of alcohol fuels, enzymatic treatment of animal feeds for hydrolysis of pentosans, manufacturing of dissolving pulps yielding cellulose, and bio-bleaching of wood pulp [Detroym R. W. In: Organic Chemicals from Biomass, (CRC Press, Boca Raton, Fla., 1981) 19-41; Paice and Jurasek, J. Wood Chem. Technol. 4: 187-198; Pommier and Fuentes, 1989, Tappi Journal 187-191; Senior et al., 1988, Biotechnol. Letters 10: 907-9121].
Xylan is abundant in plant cell walls. Arabinoxylan, in particular, is abundant in grains, such as wheat, barley and rye. Soluble forms of arabinoxylan render aqueous mashes of these grains highly viscous. Xylanases break down (arabino)xylan and release short chain, soluble sugars. Xylanases, such as those from GH Family 5, 8, 10 and/or 11, may be used in bioethanol applications to reduce viscosity and improve yields of fermentable sugars. However, cereal grains produce inhibitor proteins that bind many microbial xylanases rendering them ineffective.
EP695349 discloses a GH10 xylanase from Aspergillus aculeatus. 
WO2006/078256 discloses a GH10 xylanase from Aspergillus fumigatus. 
The present invention provides variants of a xylanase with improved properties compared to its parent enzyme.